Different between Synchronization and Asynchronization

Asynchronous process: It allows the partitioning of the work, the scheduling of threads, cancellation support, state management. It maximizes the performance of your code while focusing on the work that your program is designed to accomplish.  (Ref: msdn). For example: multiple cores in CPU. Different action process done at the same time with differnt cores.
Synchronous: Works perform in sequence. A thread that finish and then other thread can start. one core in CPU. can do one action process at one time.

In more details. [Synchronous] LINQ. IEnumerable or IEnumerable<T> data source, and have deferred execution, which means they do not begin executing until the query is enumerated.  [ASynchronous]The primary difference is that PLINQ attempts to make full use of all the processors on the system. It does this by partitioning the data source into segments, and then executing the query on each segment on separate worker threads in parallel on multiple processors.